Why do hurricanes get more intense? The clues lie in these huge Caribbean currents

Eddies exist across the world’s oceans and can help fuel hurricanes. A new University of Miami study found that some in the Caribbean may contain a barrier, created when South American rivers dump massive plumes of freshwater into the ocean and prevent deeper cooler water from mixing with warm surface waters. NASA

Eddies exist across the world’s oceans and can help fuel hurricanes. A new University of Miami study found that some in the Caribbean may contain a barrier, created when South American rivers dump massive plumes of freshwater into the ocean and prevent deeper cooler water from mixing with warm surface waters. NASA

Massive ocean eddies rolling across the Caribbean may contain a hidden layer that fuels hurricanes, according to a new University of Miami study that for the first time documents the phenomenon.

The discovery, by a doctoral student at the Rosenstiel School of Marine and Atmospheric Science and published in the Journal of Geophysical Research last month, has the potential to help improve one of the trickiest features in hurricane forecasting: projecting a storm’s intensity.

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Oceanographers have long known eddies influence hurricanes. Every six months or so, the Loop Current flowing into the Gulf of Mexico off the Yucatán cuts off to form an eddy that drifts into Texas. The eddies contain warm cores that can strengthen hurricanes feeding off warm water.

125 milesThe width of a massive ocean eddy found with a hidden layer that can help fuel hurricanes

A current carrying warm water north off the coast of South America creates similar eddies in the open ocean. But little research has been done on how they affect hurricanes or whether they influence the kind of rapid intensification that last year fired up Hurricane Matthew, with its sustained winds increasing by about 83 mph in less than 24 hours to become a powerful Category 5 storm packing 160 mph winds. The storm left hundreds dead in Haiti, skirted the Florida coast and caused massive flooding and nearly 50 more deaths in the Southeastern United States.

Johna Rudzin used satellite imagery to identify one Caribbean eddy south of Haiti in September 2014, then designed an experiment that focused on the surface waters down to 165 feet — the zone that interacts with hurricanes. In a single day, she and a National Oceanic and Atmospheric Administration flight crew flew over the 125-mile-wide eddy and dropped 55 sensors to measure temperature, salinity, density and other variables.

What they discovered was surprising, and a first.

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Unlike eddies in the Gulf of Mexico, the ocean eddies had a different structure. The water was fresher at the surface because of an enormous summertime plume flowing from the Amazon and Orinoco rivers off the coast of South America.

That lighter and warmer freshwater sat on top of a denser saltwater layer that essentially acted as barrier — preventing mixing that can bring cooler water to the surface and weaken a hurricane.

This affects hurricane intensity because they thrive off warm sea surface temperatures.

While Rudzin’s study examined just one eddy, she’s hoping additional research will determine whether the pattern is consistent, which could then be fed into computer models that project intensity.

“This is just one case, one eddy,” she said. “Being able to sample before, during and after a hurricane would provide a wealth of knowledge about what happens ... and how these eddies affect hurricane intensity.”

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